In a foil-bag producing process, at least two foils are supplied that serve as side foils of the foil bag. The foils are normally supplied by corresponding supply rolls. The individual foils are placed one upon the other and are sealed or bonded to each other at least at the place where the side edges of the foil bags are positioned. The interconnected foil webs are then cut along the connections to form individual foil bags. A bottom foil which in the area of the future bottom of the foil bag is sealed or bonded between the side foils and provides space for the filling material when being folded apart can be placed between the side foils. Moreover, such a bottom foil functions as a standing base. Subsequently, the foil bags which are produced in this way and are closed at three side edges can e.g. be supplied to a filling station in which the filling material is filled in through the fourth edge that has not been closed yet, and this fourth edge of the two side foils is then sealed or bonded.
As a rule, the foil webs which are supplied to the sealing means are already provided with corresponding imprints which furnish information about the product to be contained in the foil bag. For instance, it is exactly determined for each individual foil web already before it is supplied to the sealing or bonding means how much foil material is respectively provided for a foil bag. However, there might be slight variations in the amount of foil material intended for a foil bag. Such variations may e.g. be caused by an unprecise printing machine for forming the imprint. Moreover, the unwinding operation which is carried out on the supply roll might lead to different extensions of the foil material, depending on whether a great or small amount of foil material has been wound onto the supply roll. In view of the large outputs which are nowadays standard in automated production systems, such variations, even though they are small as such, accumulate in an additive manner, possibly resulting in an undesired displacement of the printed pattern relative to the side edges of the future foil bag. Such a problem will be all the more serious if, in addition to the imprint, there are other features provided for, e.g. an insertion hole for a straw in a foil bag for beverages where the straw is displaced with respect to its correct position.